hymen

https://doi.org/10.1351/goldbook.10821

Thin, membranous fold of highly variable appearance that, before its rupture, partly occludes the opening of the vagina.

Source:
PAC, 2016, 88, 713. (Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)) on page 766 [Terms] [Paper]